1. Field of the Invention
The invention relates generally to the lifting and leveling of precast concrete slabs for use in the construction or repair of concrete surfaces.
2. Description of the Related Art
Precast concrete slabs are commonly used in the construction and repair of concrete surfaces such as concrete roads. Precast concrete slabs are lifted and placed in excavations and then leveled to be even with adjacent slabs. Grout is then pumped underneath the slab to fill and solidify any voids. It is common for precast concrete slabs to have lifting anchors embedded in the concrete so that the slabs may be lifted by a crane and rigging system. The slabs are leveled using precise surveys and excavation, plastic leveling shims, grout leveling pads or a process known as “mud jacking”; however, these leveling techniques can be costly and time consuming.
U.S. Patent Application US2014/0053475 discloses a leveling lift device embedded in the corners of a precast concrete slabs to aid in the lifting and leveling of the precast concrete slabs. The leveling lift device includes a flat base plate, a section of pipe affixed to and standing upwardly from the base plate, a threaded hollow sleeve sized such that the bottom is removably received within the upstanding pipe and a threaded end that is removably received in the upper portion of the threaded hollow sleeve.
When the leveling lift device is embedded into the concrete slab, the base plate is located along the bottom of the slab, the threaded hollow sleeve extends through the slab between the top and the base plate and the threaded end cap is threaded into the threaded sleeve to protect the threads on the threaded sleeve. The end cap has a head which sticks above the upper surface of the concrete slab so that the end cap can be removed after the slab is formed. To lift the slab, the end cap is removed and a threaded bolt is inserted through a lifting device and into the threaded hollow sleeve to secure a lifting device to the slab. The lifting bolt is long enough to extend the length of the threaded shaft to a base plate and to extend above the upper surface of the cement slab. To level the panel, the threaded bolt is rotated in the threaded sleeve until it contacts the base plate wherein further rotation applies a pushing force against the base plate, elevating the slab above as necessary to make the slab level with adjacent slabs. When the slab level, the lifting device and threaded bolt are disposed above the top surface of the panel and grout is pumped beneath the panel to fill the space between the panel and the surface below. After allowing the grout or cement to cured, the threaded bolt and lifting device must be removed from the threaded sleeve and grout or cement must be pumped into the threaded sleeve to fill the void left by the lifting bolt.
The lifting and leveling device presents problems during installation and use, including that the threaded end cap and separate threaded bolt increases the likelihood of misplaced parts during installation. Also, the threaded bolt is always disposed above the surface of the concrete slabs during lifting and leveling, presenting tripping hazards. The lifting and leveling device also requires removing the end cap, inserting the threaded bolt and lifting device and then subsequently removing the threaded bolt and lifting during casting, lifting, leveling and grouting, which adds significant time to the construction or repair of concrete surfaces using precast concrete slabs. The grout beneath the slab must cure before removing the threaded bolt, which is required, also adding time the construction or repair. Furthermore, filling the threaded sleeve with grout or cement prevents subsequent use of the leveling lift device.